Hydrosilylation chemistry, involving the reaction between a silylhydride and an unsaturated organic group, is the basis for synthetic routes to produce commercial silicone products such as silicone surfactants, silicone fluids and silanes. Conventionally, hydrosilylation reactions have been catalyzed by precious metal catalysts, such as platinum or rhodium metal complexes.
Various precious metal complex catalysts are known in the art. For example, U.S. Pat. No. 3,775,452 discloses a platinum complex containing unsaturated siloxanes as ligands. This type of catalyst is known as Karstedt's catalyst. Other exemplary platinum-based hydrosilylation catalysts that have been described in the literature include Ashby's catalyst as disclosed in U.S. Pat. No. 3,159,601, Lamoreaux's catalyst as disclosed in U.S. Pat. No. 3,220,972, and Speier's catalyst as disclosed in Speier, J. L, Webster J. A. and Barnes G. H., J. Am. Chem. Soc. 79, 974 (1957).
Although these precious metal compounds and complexes are widely employed commercially as catalysts for hydrosilylation reactions, they have several distinct disadvantages. One disadvantage of the conventional catalyst systems is the undesired color imparted to the final product. This yellow coloration or Pt precipitation in crude products often necessitates additional and costly purification steps. Another distinct disadvantage of the conventional systems is the progressive deactivation of the platinum catalysts during the course of the reaction which necessitates higher loadings of this costly metal.
Due to the high price of precious metals, catalysts derived from these platinum metals can constitute a significant proportion of the cost of organosilane and silicone products. Over the last two decades, global demand for precious metals, including platinum, has sharply increased, driving prices several hundred folds higher, thereby precipitating the need for effective, yet lower catalyst loadings. There is a need in the silicone industry for platinum catalysts of improved stability. This improved stability would enable the lowering of Pt catalyst loadings and decreasing cycle time in reactors and improving yield for many hydrosilylations.
The use of pre-formed Pt-COD complexes (COD=1,5-cyclooctadiene) in hydrosilylation reactions has been previously reported, e.g., L. Lewis et al., Organometallics, 1991, 10, 3750-3759, and P. Pregosin et al., Organometallics, 1988, 7, 1373-1380. PtCODCl2, PtCODMe2, and PtCODPh2 are commercially available and their use as catalysts for hydrosilylation has been known for many years. Roy et al. have reported the preparation of a series of PtCOD(SiR3)2 compounds from PtCODCl2 (Roy, Aroop K.; Taylor, Richard B. J. Am Chem. Soc., 2012, 124, 9510-9524; and U.S. Pat. No. 6,605,734).
Pt-COD complexes with catecholate or amidophenolate ligands have been reported (Boyer et al. Inorg. Chem 2009, 48, 638-645.; Richmond et al, J. Chem. Crystallogr. 1996, 26, 335-340). These papers describe the redox reactivity of these Pt complexes with non-innocent ligands. The use of these platinum-diene complexes with chelating dianions in hydrosilylation reactions producing organofunctional silanes and fluids has not been reported.
There is a need in the silicone industry for platinum catalysts of improved stability as industry work-horse catalysts such as Speier's and Karstedt's are prone to partial deactivation via agglomeration, especially at elevated temperatures of use. Improved stability of the active catalyst would enable the lowering of Pt catalyst loadings. In addition to improved stability, catalysts that demonstrate rapid activation and high hydrosilylation activity at elevated temperature are especially sought. Lastly, platinum catalysts are needed that have improved solubility in industrially-preferred organic solvent or silicones. The present invention provides one solution to these needs.